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From: jevans@cpsc.ucalgary.ca (David Jevans)
Newsgroups: comp.graphics
Subject: Re: Village Idiot asks about Ray Tracing
Summary: refraction
Message-ID: <304@cs-spool.calgary.UUCP>
Date: 7 Dec 88 23:36:19 GMT
References: <859@amethyst.ma.arizona.edu> <3324@uoregon.uoregon.edu>
Sender: news@calgary.UUCP
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In article <3324@uoregon.uoregon.edu<, markv@uoregon.uoregon.edu (Mark VandeWettering) writes:
< }<	Finally, has anyone come up with a raytracer whose refraction model
< }< takes into account the varying indicies of refraction of different light
< }< frequencies?  In other words, can I find a raytracer that, when looking
< }< through a prism obliquely at a light source, will show me a rainbow?
< }
< }     This could be tough. The red, green, and blue components of monitors
< }only simulate the full color spectrum. On a computer, yellow is a mixture
< }of red and green. In real life, yellow is yellow. You'd have to cast a
< }large number of rays and use a large amount of computer time to simulate
< }a full color spectrum. (Ranjit pointed this out in his article and went
< }into much greater detail).
< 
< Actually, this problem seems the easiest.  We merely have to trace rays
< of differing frequency (perhaps randomly sampled) and use Fresnel's
< equation to determine refraction characteristics.  If you are trying to
< model phase effects like diffraction, you will probably have a much more
< difficult time.

This has already been done by a number of people.  One paper by
T. L. Kunii describes a renderer called "Gemstone Fire" or something.
It models refraction as you suggest to get realistic looking gems.
Sorry, but I can't recall where (or if) it has been published.  I have
also read several (as yet) unpublished papers which do the same thing in
pretty much the same way.

David Jevans, U of Calgary Computer Science, Calgary AB  T2N 1N4  Canada
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